4.1 STOCK ESTIMATES
The estimated stock density of T. maxima was moderately high (1745 Tm/ha) but disturbingly low for T. squamosa (0.82 Ts/ha) at Fakaofo Atoll. At Nukunonu Atoll the estimated stock density of T. maxima was very high (6860 Tm/ha) but the stocks of T. squamosa were even more deplorable than at Fakaofo (0.41 Ts/ha). At Atafu Atoll the estimated stock density of T. maxima was moderate (841 Tm/ha) but a most serious condition for stocks of T. squamosa exists as no live specimens were seen during the survey. The highest densities of T. maxima at single tow sites at each of the atolls were: Fakaofo, 28,116/ha; Nukunonu, 26,400; Atafu, 5,430/ha. Natural stock densities of this species have been recorded from several places where numbers are very high, ie., One-Tree Island, Great Barrier Reef, Australia - 8000 Tm/ha (McMichael, 1975); Takapoto lagoon, Tuamotu archipeligo (French Polynesia) where various sampling sites were from 12,800–60,000 Tm/ha (Richard, 1978; Salvat and Richard, 1985); Abaiang Atoll, Central Gilbert Islands, Kiribati - low density sites at about 100/ha whilst high density sites were 5000–10,000 Tm/ha (Munro, 1986). Low densities of T. maxima were found in north Tarawa lagoon (0.7–31.7 Tm/ha) but densities of this species were not regularly quantified in Munro's (1986) survey because their main concern was to survey the larger species of giant clams. The densities of T. maxima found in the Tuvalu survey (Braley, 1988) were very modest (63–101 Tm/ha in the three atolls surveyed…Nukufetau, Nukulaelae, Funafuti). The densities of T. squamosa in the Tuvalu atolls was very low (0.68–1.4 Tm/ha) similar to the levels found here in Tokelau. The proportion of T. maxima of the two species was over 99.9%. This proportion is much greater than the survey done in Tonga (McKoy, 1980) and even greater than the proportion of these two species found in Tuvalu (Braley, 1988). This may be a result of T. squamosa being at the edge of its range in Tokelau, the high densities of T. maxima, and/or a long history of overfishing of this larger species of clam.
I suggest that a resurvey be carried out in 1999 to compare the results of tows from the same areas covered in this survey. The present survey results will act as a baseline to compare with future studies. If a resurvey is carried out in 1999 it will be important that the tow method be consistent with this survey.
4.2 STATUS QUO OF FISHING INTENSITY
The average consumption rate of clams is about 1 – 2×/month/person in all of the atolls. This is slightly less than consumption rate in 2 of the 3 Tuvalu atolls (Braley, 1988). It appears that Tokelauans will generally always obtain fish before they will take clams for food. Traditionally, clams have been used as a standby seafood source when the seas are very rough and they are unable to fish outside the reef. Gillett and Toloa (1987) divided seafood consumption at Fakaofo into an Inshore category [including tridacnid clams] and Tuna/tunalike fish category. Over a one month period they found that the Inshore category made up 64.5% of food consumption, Tuna about 11–16% and other non-seafood sources made up the remainder. Unfortunately, they were not able to subdivide the Inshore category with its 39 species of reef, lagoon or bottom fish and invertebrates. Relative to the populations of people on Fakaofo and Nukunonu, the consumption rate of clams does not appear to be too high to threaten the T. maxima populations, but the populations of T. squamosa are under serious threat from clam fishermen. In Atafu, the population of T. maxima is more pressured by local consumption than at the other atolls, and the effect on the population of T. squamosa is most evident. Without doubt, the largest threat to T. maxima and T. squamosa populations on all three atolls is continued collection of clams for export to Western Samoa. If this fishing were unregulated or if regulations were not enforced, it could lead to the eventual demise of the healthy populations of T. maxima presently existing in the lagoons and total extinction of T. squamosa.
The fishing pressure on T. maxima was shown graphically on size-frequency histograms, where the mean size of clams on Akau Loa [reef just off the village at Nukunonu] was significantly smaller than clams measured from either the south or north ends of Nukunonu lagoon. The same evidence for fishing pressure was shown for Nukufetau atoll in Tuvalu (Braley, 1988). On average, the size of clams in Atafu were a little larger than those of Fakaofo or Nukunonu. This may be related to the lower densities seen in Atafu and possibly more nutrients in Atafu lagoon than the other atoll lagoons [the lagoon clarity in Atafu was considerably less than any part of Fakaofo or Nukunonu lagoons indicating a greater tendency toward eutrophication in Atafu lagoon].
4.3 REEF RESOURCES CONSERVATION AND MAINTENANCE OF CLAM POPULATIONS
The stocks of T. squamosa [fahua taka] are extremely low in Fakaofo, Nukunonu and Atafu. It would be fair to say that the breeding stock of this species is at a critical level for its survival. One need only look at the case of the total extermination of stocks of H. hippopus from Tonga, Fiji and W. Samoa, and of T. qiqas from Fiji (and probably Tuvalu) in recent times to know that this situation is serious. I suggest that as a preliminary step the Council of Elders on each island discuss these recommendations and hopefully will give total support for a programme to manage the stocks of clams, particularly T. squamosa. Stocks of adult T. squamosa should be collected [not held for longer than 2 hrs. in a boat with seawater regularly rinsed over them and with shade from the sun to cover them] from the lagoon and brought to 1 or 2 locations where they will be placed in groups of at least 50 clams. The clams should be placed about 1m apart in a block grouping or possibly in a double circle where the excurrent siphon is facing toward the centre of the circle. This would encourage mass spawning of the broodstock because they will be close enough for the chemical signals of spawning to induce the spawning reaction from clam to clam. Most importantly, the eggs and sperm will be in sufficient quantities to fertilise the eggs successfully and give the best possible chance for enhancing the success of the progeny to repopulate the lagoons. The penalty for taking any of these broodstock should be severe to discourage any poaching. Also, it might be wise to have the Council of Elders ask a number of men from the village to spare some of their time to assist in collection of these broodstock clams. The effort put in by these men to collect the clams should pay off by discouraging others from illegal poaching. The sites for Fakaofo, Nukunonu and Atafu are noted on the xerographic-reduced aerial photographic maps of these atolls. Two sites would be better than one to help assure successful reproduction and population increase. When new juveniles of T. squamosa are found to be growing in shallow water they should be allowed to reach a large size before harvest, thus assuring that these individuals have a chance to reproduce before they are harvested. The average maximum size of this species is about 40cm shell length so it would be wise to put a ban on the taking of T. squamosa smaller than 20–25cm shell length. With this restriction, the larger clams can be taken [except for the 100 or more clams collected for the 1 or 2 broodstock holding sites, many which may be larger than 20–25cm.]. The depth of these holding sites should be relatively shallow (ie. 6m) to allow the broodstock clams to receive maximum light. Although only speculative at the moment, it is assumed that such an optimal position for light would result in the most high quality eggs.
The stocks of T. maxima [fahua nao] are not endangered as is the case with T. squamosa. The collection for export to W. Samoa has already been restricted by the Council of Elders in Fakaofo, Nukunonu and Atafu. It is wise to place some type of restriction on this export of a limited marine resource. I do suggest that certain areas with high densities of T. maxima be set aside as breeding sanctuaries for this species of clam. It would not hurt any fisherman to avoid a specific area and collect clams from areas adjacent to these reserves. It would be difficult to stop people poaching from such a reserve when it is far from the village but with the support of the Council and by placing some kind of markers on the adjacent reef tops to designate the area, one could only hope that most fishermen would leave the area free from collection. If two areas in different parts of the lagoon are set aside as clam reserves, this would help assure future recruitment of this species in the lagoon. In ten years the areas adjacent to the sanctuaries may have significantly fewer clams due to collection and the importance of the reserves to breeding stock will be then very apparent. If fishing pressure does not increase greatly from its present level, then the reserve areas may contribute to recruitment in adjacent areas so there may appear to be little change in density of clams.
Several questions were asked of villagers in the questionaire survey which were related to reef resource conservation (see Appendix, questions 4a, 4b, 6, 7a, 7b, 8) to gauge their awareness of marine resources and some basic ecological principals. The questions are also valuable for the local governments of Tokelau to assess how village people would feel about restrictions related to the reef and food collection.
It is concluded from the answers that there were no traditional taboos or customary laws regarding the taking or use of giant clams. The recent restrictions/license requirement put on collection of clams for export to Samoa by the Council of Elders at each atoll was mentioned by only some interviewees. Anthony Hooper (1984), who has carried out work on the cultural aspects of fishing in Fakaofo for 30 years said: “Again, traditional Tokelau fishing in fact had no explicitly conservationist strategies. There are no closed seasons, no prohibited areas, nor any of the other conservationist measures mentioned by Johannes (1978) as characteristic of traditional Pacific Island fisheries that remains the case in the 1980s.” Hooper mentioned the UNDP-supplied freezers left on the ship and used to ship clams to Samoa. His conclusion on giant clams was: “Regarding marine resources…The one resource which has been depleted is Giant clams. Formerly regarded as a sort of ‘emergency’ resource to be tapped mainly when storms and rough weather made other forms of fishing difficult, the new export ‘market’ has meant that they are taken much more regularly, and men complain that they ‘now have to dive for them’.”
On Fakaofo, Nukunonu, and Atafu there were 75.3%, 71.6%, and 55%, respectively, of the interviewees who believed that giant clams were becoming scarcer. This is in constrast to answers in Tuvalu (Braley, 1988) where the majority of people in 2 of 3 atolls believed clams are not becoming scarcer or there is no change from the past. Nevertheless, there was still a widespread belief that by cutting the clam out of its shell with a small knife, the divers were releasing some eggs and it would help the clams to reproduce. Here, as in Tuvalu [where the belief was that leaving the byssal attachment would produce more baby clams] this belief justifies unrestricted fishing of the clam populations. It was most interesting that most people believed that T. squamosa was only an older and larger T. maxima. They did not realise that these two separate species would not breed. With this new understanding, the low population level of T. squamosa can be clearly seen to be in danger of extinction.
Responses which suggested that restrictions should be made on fishing of clams were voiced by 56.3% (Fakaofo), 80.5% (Nukunonu), and 37.8% (Atafu) of the interviewees. A higher proportion of people saw a connection between taking adult clams and a reduction of clams on the reef in the future than was found in the Tuvalu survey (Braley, 1988).
In general, I sense an interest in Tokelauns wanting to better understand how to manage their marine resources, in particular.
4.4 POTENTIAL OF CLAM MARICULTURE IN TOKELAU
There is still no large-scale commercial cultivation of giant clams but successful smaller-scale rearing of giant clams from eggs to ocean-farmed juveniles and adults has been in practice since the early 1980s (Heslinga et al., 1984; Crawford et al., 1986; Braley et al., 1988). Much of the work has been concentrated on the two largest species of giant clam, T. gigas and T. derasa, but considerable work has also been accomplished with rearing T. squamosa, H. hippopus and H. porcellanus (Palau, Australia, Philippines, Papua New Guinea).
Given the serious state of the T. squamosa populations in Tokelau, it may be in the interest of Tokelau to consider cultivation of this species. Nearly 100% of all people interviewed in the village questionaire survey wished to see the Tokelau government begin experiments on the culture of giant clams. I recommend that the Director of Agriculture and Fisheries (Tokelau) should hold discussions with Mr. Lui Bell, Biologist (and Acting Head) of Fisheries Division, W. Samoa to see how they may be able to collaborate on a joint project of rearing T. squamosa. A hatchery facility was built by the Japanese (late 1970s) at the Fisheries Division site in Apia and it has most recently been used by Mr. Bell to spawn and rear T. squamosa. If Tokelau and W. Samoa would collaborate on this, an international funding agency could be approached to provide funding to update the existing facility for production of more clam juveniles which would be grown out both in W. Samoa and in Tokelau. A Tokelauan hatchery assistant could work at the hatchery in Apia along with Samoans. Broodstock T. squamosa are very rare in W. Samoa so that it would be of mutual benefit to Tokelau and W. Samoa if some broodstock T. squamosa could be collected in Tokelau and sent by ship (MV Wairua) in a seawater flow-through container to the hatchery in W. Samoa. In exchange, to begin with, some of the 1.3 year old juvenile T. squamosa reared from eggs at the Apia facility could be sent up to Tokelau for growth trials [in cages]. It would be much more economical to run a single hatchery for the two countries than to try to set up a new one on Tokelau.
The ACIAR-JCU Giant Clam Project is planning a training course on giant clam culture in North Queensland during January-February 1990. This will involve other Pacific Island nationscollaborating with the ACIAR-JCU project. There will be space for Mr. Mose Pelasio at the training course if Tokelau Affairs is able to find funding for him (the ACIAR-JCU project has only budgeted for countries which are presently involved with the project). It is suggested that FAO-SPADP (Mr. Tanaka) in Fiji be approached to cover funding for Mr. Pelasio. FAO-SPADP has funded a number of Pacific islanders to go to the clam training course at MMDC, Palau.
There are many suitable sites for growout of clams within the lagoons of the Tokelau atolls. Culture can be done subtidally or intertidally. The clarity of the water and limited filamentous algae seen in Fakaofo and Nukunonu lagoons would make subtidal culture as appealing as the intertidal culture which has been pioneered in North Queensland. Subtidal culture may be slightly preferable over intertidal culture for T. squamosa.
While in Tokelau I was approached by many people about the possibility of Tokelau obtaining specimens of the largest giant clam species, T. gigas. It appears that the closest this species was found to Tokelau was in Tuvalu (see Braley, 1988). It is no longer found live in Fiji (or Tuvalu) but is still found live in the Gilbert group of Kiribati. It is not known whether the Phoenix group of Kiribati (directly north of Tokelau) has T. gigas. It may be possible for hatchery-reared juvenile clams of this species to be sent to Tokelau from Australia or the Solomons if requested by Tokelau. Large adult broodstock may be brought by ship (on deck in large containers with flow-through seawater) from the Phoenix group [dependent on if this species is found there and upon discussions with the government of Kiribati]. Such an expedition would have to be planned carefully to complete in a minimum of time for both the economic reason and to maximize survival of collected adults. The outside of the shells would have to be scrubbed clean and disinfected with a chlorine bleach dilution to remove any external unwanted marine organisms. The imported adults could be set in a group for spawning purposes and any juveniles that recruit onto the lagoon reefs would have to be protected from harvest for many years to allow the population to increase. If clams were to be imported from a group of atolls close to Tokelau there would be only a very small chance of any clam disease or parasites being introduced to Tokelau. This issue will require thought and discussion before a decision should be made.
4.5 PEARL OYSTER INTRODUCTION TO TOKELAU
As mentioned earlier, several South Pacific Fisheries consultants have visited Tokelau and made comments on the potential of Tokelau lagoons for culture of pearl oysters (van Pel, 1958; Hinds, 1971; Laboute, 1987). Coeroli (in Salvat and Richard, 1985) discussed the mother-of-pearl fishery in Takapoto lagoon, French Polynesia. He noted that in the mid-1950s reserve zones were created for breeding stock and annual fishing quotas were set throughout the Tuamotu atolls. A rapid decline in natural oyster beds has occurred in most atolls with Takapoto the exception because the protection measures were strictly adhered to, and Takapoto has a large number of emerged coral pinnacles and submerged types [dead parts are able to be colonised by the pearl oysters] which enhance recruitment. Here, the mean density of pearl oysters is 0.1/m2. Laboute (1987) found the coral pinnacles and closed type atoll of Fakaofo to be strikingly similar to Takapoto. The description of suitable conditions for pearl oysters in Takapoto and my observations in Fakaofo would at first suggest that Fakaofo may indeed be a good atoll to attempt an introduction of pearl oysters. There are numerous pinnacles of both the emerged and submerged type in the lagoon and a considerable percentage of this coral is dead (80–90%). However, the extremely high densities of spondylid (spiny or thorny) oysters (32–56/m2) found on the slopes of patch reefs in the centre of Fakaofo lagoon (down to 36m) are a potentially unbeatable competitor for the goal of establishing natural populations of introduced pearl oysters. The microalgae filtered from the water by the spondylids is likely to be exactly the same food source required by pearl oysters; the filtration by the spondylids and the numerous solitary tunicates may also pick up competent larvae ready to settle and kill them in the process; the space available may not allow for pearl oysters to settle and grow. There are many dead coral pinnacles nearer the perimeter of the lagoon where space for settlement would present no problem but predation may also be a problem. Therefore, I would recommend that an introduction of pearl oysters be seriously discussed with the Council of Elders at each atoll and determine to what extent this project should be carried out.
Some pearl oysters were found by people on each atoll but this is a rare event. According to Gillett (1985) the pearl oyster has never been plentiful but is rare at present. It was used in the Tokelau pearl-shell lure for shipjack tuna fishing. Gillett (1985) suggested that the introduction of diving goggles to Fakaofo in the 1940s was the main factor contributing to the demise of the pearl oyster population today.
I would suggest that if the government decides it wishes to attempt an introduction of pearl oyster, that this be done in Fakaofo lagoon and/or Atafu lagoon. Fakaofo has abundant coral patch reefs, bommies, pinnacles and a ‘lagoon within the lagoon’ at the southern end of the atoll where the pearl oysters could be held. Atafu is a small lagoon and still has considerable coral areas, though not as much as Fakaofo, may have more natural microalgae in the water column for the pearl oysters to feed on, and there are much lower numbers of spondylid oysters than in Fakaofo. Nukunonu has the lowest density of spondylid oysters but the water is clearest (lower levels of microalgae likely), fewer coral patch reef, pinnacles, etc. than at Fakaofo, and the lagoon is almost twice the surface area of Fakaofo. Such a large volume of water (much of it deep) may not be conducive to recruitment of pearl oysters. There were 2 areas marked by van Pel (1958) in each of Fakaofo and Atafu lagoons where he suggested pearl oysters be located. In Fakaofo the sites are in the south end (inside the ‘lagoon within the lagoon’) and on the mid-eastern side. In Atafu he suggested the southeast end (close to where I have suggested a clam reserve be established) and on the mid-north-east side.
Hinds (1971) suggested that 5000 pearl oysters would be needed for a transfer to Tokelau by a suitable vessel fitted with holding tanks and flow-through seawater. Sims (personal communication) suggested that not less than 1000 pearl oysters per island would be needed, with a maximum of 5000–10,000 if the lagoons look very good. Penrhyn with a good airstrip, wharf and deep passes into the lagoon may be the best choice of a supply of mother-of-pearl. Manihiki has more pearl oysters but it is harder to get to (ie. no passage, small airstrip). Although there is now purportedly a black-lipped pearl oyster hatchery in Okinawa producing spat, it is advisable to try to get broodstock adults from the northern Cook Islands. The Cooks are closer to Tokelau and there should be less chance of new parasites, bacteria or virus coming to Tokelau with the Cook Island oysters than if oysters were to come from as far west as Okinawa. One has to be careful of such introductions, however, because there have been diseases of pearl oysters transferred between atolls in the Tuamotu group and the diseases have affected other bivalve molluscs.
4.6 BRIEF SUMMARY OF RECOMMENDATIONS
GIANT CLAMS:
Council of Elders at each atoll should discuss recommendations and the report; hopefully, they will be supportive of stock management.
T. squamosa should be banned from collection for food for at least 5 years. Adult specimens of this species should be collected from the lagoon (with care described earlier) and concentrated into clusters (of about 50) to enhance reproductive success. After a given time period when the ban on this species is lifted, there should be a minimum size limit established for this species. Clams smaller than 20–25cm shell length should not be taken so that these have a chance to breed before they are harvested at sizes over 20–25cm. The large permanent broodstock collected for breeding clusters must continue to be protected regardless of their size.
At least 2 marine reserves should be established in each atoll lagoon for T. maxima. Proposed areas have been marked on the maps of the atolls (Figs. 2, 4, 6). No fishing of clams will be allowed in these reserves perpetually. If this is not considered suitable on a perpetual basis it must be protected from fishing for at least 10 years to assess the result in a future resurvey.
If culture experiments are desired it is suggested that discussions be held with Mr. Lui Bell, Biologist (and Acting Head) of Fisheries, W. Samoa, regarding a combined effort at culturing T. squamosa at ther W. Samoa Fisheries facility and shipment of juvenile clams to Tokelau for trial growout studies. It would be mutually beneficial if Tokelau could provide some live broodstock of this species which would be spawned in the W. Samoa hatchery to produce seed clams for growout in both W. Samoa and Tokelau.
Mr. Mose Pelasio should come to a training course on giant clam culture in North Queensland, Australia; this is being planned for January/February 1990 (6 wks.) and it will involve other Pacific islanders whose Fisheries divisions are already collaborating with the ACIAR-JCU Giant Clam Project. Funding may be sought for Mr. Pelasio from FAO-SPADP, Fiji.
A resurvey should be made in 1999 at the same tow sites and using the same survey methods. This resurvey will also assess the effect of clam reserve areas.
PEARL OYSTERS:
The introduction of pearl oysters may be expensive and the pearl oysters may not be able to establish their population in the lagoons because of several factors. Foremost in Fakaofo lagoon is the high densities of spondylid oysters which would be stubborn competitors of an attempt to establish pearl oysters.
If a small or large-scale pearl oyster introduction is attempted, the pearl oyster stock should probably come from Penrhyn or Manihiki in the northern Cook Islands rather than Okinawa, Japan. There is likely to be a greater chance of unwanted pests associated with pearl oysters from Okinawa.
Two sites at each of Fakaofo and Atafu were suggested by van Pel (1958) to place introduced oysters; I agree with these two atolls and the sites.
If the introduction is attempted it should be given careful attention and Mr. Neil Sims should be sought as a consultant.
